Separation of metallic sulfids.



UNITED STATES PATENT OFFICE.

LESLIE BRADFORD, 0F BROKEN HILL, NEW SOUTH WALES, AUSTRALIA.

SEPARATION OF METALLIC SULFIDS.

No Drawing.

This invention relates to improvements in the separation of mixedsulfids more particularly to the separation of mixed lead and zincsulfids, but it will be understood that I do not confine myself to thetreatment of. these mixed sulfids.

The object of this invention is to provide a process of effecting apreferential or selective separation by meansof flotation of certainparticles such as zinc sulfid (blende) 'or pyrites, or both, from sulfidparticles of lead (galena) obtaining zinkiferous or pyriticconcentrates, or both, on the one hand and lead-containing concentrateson the other hand.

This invention is applied'to the treatment of -.ores, concentrates,tailings, residues, slimes, and other products, and the term ores inthis specification includes any mixture of metallic sulfids or metallicsulfids and gangue.

Hitherto flotation separation processes have only been generally appliedto the general purpose of separating of the metallic sulfids from thegangue. Several dif-' ferent processes have been evolved for theseparation of the zinc sulfids (blende) from the lead sulfids (galena)but these processes have been more or less dependent upon certainpreliminary treatment or upon the conditions under which the separationis effected, and as a result thereof certain of the sulfids such as thelead sulfids (galena) are permanently affected upon their surface sothatthey are rendered more or less immune or insusceptible to flotationwhile the sulfids which have not been so affected are floated andproduce the float concentrates.

According to my invention a preferential or selective flotation of thezinc sulfids (blende) or pyrites, or both, from the lead sulfids(galena) is effected by submitting the ores to flotation separation in aseparating medium by which the lead sulfid particles (galena) are notchemically'or otherwise permanently affected upon their sur-Specification of Letters Patent. Patented May 16, 1916 Application filedSeptember 10, 1913. Serial No. 789,017. I

face but by the action of the said medium itself the surfaces of thelead sulfid (galena) partlcles are brought into direct contact with themedium and the particles are wetted and thus temporarily rendered immuneor insusceptible to flotation.v while the other sulfids float. Incontradistinction to the processes previously mentioned the lead sulfidparticles (galena) are not permanently affected, that is to say that ifthe said particles are subjected to a further flotation separation inthe presence of a medium which does not of itself wet the surface of thesaid particles then they aresusceptible to flotation and floatconcentrates may be ob tained.

'I find that a preferential flotation can be obtained of zinc sulfids(blende) or pyrites, or both, from lead sulfids (galena) by submittingthe ores to flotation separatlo'n in a medium comprising a solution(preferably a solution feebly acidulated) of one or more chlorids of ethe alkaline metals or alkaline earths.

I will now proceed to illustrate generally the application of thisinvention. The ores or concentrates are ground to a state. of finedivision and slimed when found necessary to disassociate the differentsulfid particles from each other and from the gangue. The groundmaterial is then submitted to a flotation separation (preferably anagitation or aeration flotation separation in which a frothing agent,such as oleic acid with heat is employed) in a vmedium consistingpreferably of a solution of sodium chlorid acidulated .With sulfuricacid or other commercial acid. Inthe treatment of mixed sulfid floatconcentrates Which are the product of the ordinary acid flotationtreatments in the wetting medium (e. g. the saline solution) may be usedin a neutral or alkaline condition in which case I findthat the floatconcentrates usually require retreatment for the efiective division ofthe sulfid particles.

I prefer to have the flotation medium at a temperature ranging from 120F. to 160 F. for Ifind that at this temperature the preferential.separation of the zinc sulfid (blende) or pyrites, or both, from thelead sulfid (galena) takes place most effectively but in'some cases apreferential separation' may be effected at lower temperatures and evenat atmospheric temperature, but usuallythe float zinc concentratesproduced at these lower temperatures require retreatment.

. The quantity of acid which is added to the wetting medium (6; g.saline solution) has an important bearing upon the preferentialseparation effected by this process. I am unable to indicate the degreeof acidity required for all ores, but with certain ores with which Ihave experimented I find that if the acidity of the saline solution isincreased to one per cent (1%) or thereabout the lead sulfid (galena)particlesfloat more or less completely in addition to the zinc sulfid(blende) or pyrites, or both. I have found from experiments performed byme that a saline solution only feebly acidulated, that is containing 0.1per cent. or 0.2 per cent. or thereabout is suitable for my purpose.

If the process is applied directly to the preferential flotation of thezinc sulfids (blende) or pyrites, or both, from crude ores or the likecontaining lead sulfid and. gangue the zinc sulfid (blende) and/orpyrites can if desired be separated without the addition of any organicfrothing agent (such as oleic acid). The addition of a frothing agentmay however be used Without rendering the lead sulfid (galena)susceptible to flotation,

in the above described medium.

The quantity of saline substance in the preferential floating medium maybe varied within Wide limits. I find that a feebly acidulated solutioncontaining about ten per cent. sodium chlorid well answers the purpose,but I do not bind myself to these directions.

With regard to the nature of the saline salts employed I prefer to usecommon salt (sodium chlorid) owing to its cheapness. This flotationseparation can be carried out in any well known apparatus in theordinary way. I find then that a preferential flotation is effectedinasmuch as the lead sulfid (galena) particles are temporarily wettedand thereby rendered non-susceptible to flotation in the aforesaidmedium, and remain as a residue with the gangue, while the zinc sulfid(blende) or pyrites, or

both, particles are not similarly affected and nary way by any of thewell known flotation methods (preferably that known as the frothflotation process in which the ore is agitated or aerated with afrothing agent (such as oleic acid) producing mixed concentrates withoutdiscrimination of the sulfids present. These mixed concentrates are thensubmitted to the special preferential flotation separation by agitatingor aerating in the saline solution (preferably feebly acidulated)as-aforesaid whereby the lead sulfid (galena) particles become wettedand are not susceptible to flotation in such medium, and are left as ahigh grade lead-containing residue on the one hand, While the zincsulfids (blende) float producing a float concentrate high in zinc on theother hand.

In the treatment of an ore containing blends and galena with gangue,such as obtain at Broken Hill, New South Wales, I prefer to employ thesecond method above described. By applying the inevtion in this manner,both the floated zinc concentrates and the lead-containing residues arehigh grade marketable products and y can be Washed for the removal ofthe wettingmedium. A further advantage of this application of theinvention is thatthe wetting medium is maintained in a greater state ofpurity than would be possible if the herein described preferentialseparationwas applied direct to the crude ore. Lastly, thepreferredmethod of applying the invention makes it possible to produce acleaner and higher grade zinc concentrate.

In the case of ores, in a finely comminuted condition, as for example,mixed-concentrates obtained in flotation processes using an organicfrothing agent, I find that the division of zinc sulfid (blende) fromlead sulfid (galena) by the aforesaid preferential flotation treatmentis enhancedtby first submitting the concentrates to a preliminarytreatment with a grease-removing chemical for the purpose of removingany oil or oily substance or greasy hydrocarbon as by digestion in adilute alkaline solution, e. g. in a dilute solution of sodium hydrateor carbonate or other alkaline hydrate or carbonate, or by treatmentwith a solution containing a small quantity of sulfuric ether. Further Ifind that with some ores more especially those in a finely comminutedSubstances which I find are suitable for the purpose are the lowersulfur acids and their salts such as the sulfites or thiosulfates of thealkaline. metals or sulfurous acid.

Solutions of these substances are added to the medium in suflicientquantity to produce the retardation desired enabling a cleanerseparation of the zinc sulfids or pyrites, or both, from the leadsulfids. These substances must be added cautiously or the flotation ofthe zinc sulfids (blende) or pyrites, or both, will be detrimentallyaffected. The ordinary metallurgical checks will sufliciently indicatethe best working conditions.

I have.not determined all the solutions which will form a suitablewetting medium for the purpose of my invention, but the same may bedetermined before operating or using my invention by the followingsimple laboratory test :Take 100 grams of the finely crushed ore; digestsame in a dilute solution of caustic alkali, sulfuric ether or the like,then wash the ore. Both these steps are precautionary measures to removeany deleterious constituents which may be present in the ore to betested and which might interfere with the test. Transfer the ore to aglass cylinder (provided with a stopper) with a convenient amount ofboiling water; introduce the wetting reagent? and agitate. Then add asmall quantity of a ten per cent. solution of sulfuric acid and agitate.Test the liquor to ascertain whether it is acid or neutral by a drop ofmethyl orange. If neutral add little more sulfuric acid (10 per cent.solution). Again agitate and test for acidity. Continue this operationuntil a-faint permanent acidity is obtained. Then add a slight excess ofthe ten per cent. solution of acid, sufficient to bring the medium up tosay 0.1 per cent. or 0.2 per cent. strength. Add

a small quantity of a frothing agent (such as oleic acid). Agitateviolently for a sulficient length of time, and then critically inspectthe contents of the cylinder. If the wetting reagent employed in thisparticular test is found to leave the galena particles free andnongranulated, and at the same time permits the zinc sulfids (blende)particles or pyrites, or both, to granulate or coalesce together, it isan indication that the wetting reagent employed is suitable. If thistest is made by the addition of a minimum amount of wetting reagent andno differentiation between the zinc sulfids (blende) or pyrites, orboth, and the lead. sulfids (galena) is observable, repeat the test witha practical maximum quantity of the proposed wetting reagent. In thedescription of the test-above given stress has been laid on the quantityofsulfuric acid employed.

In submitting ores to the test I have found that if excessive amounts ofacid are employed the galena particles are attacked by the acid andsulfureted hydrogen gas is evolved, and this gas if present insufiicient quantity and in the presence of the frothing agent causes amore or less partial granulation of the galena particles and thus masksthe test. 7

To determine whether the wetting reagent is suitable for the purpose ofthis invention, and the quantity of same which will yield the moreeffective result, and also the degree of heat required for differentores, actual flotation separation tests must be made by first floatingthe blende or pyrites, or both, with the employment of the wettingmedium subsequently removing the remainder of the ore from the saidmedium, and

floating the galena from same by the ordinary flotation methods, andassaying the products in the usual manner.

What I claim is 1. A process for the preferential or selectiveseparation of zinc sulfids from lead sulfids in ores containing mixedsulfids which consists in submitting the ores to agitation with afrothing agent in a heated feebly acidulated solution of common salt ofsuch a nature as to render the lead sulfid particles immune to flotationwhile in the said medium but as not to'aflect the subsequent floatableproperties of the said lead sulfid particles by the ordinary flotationtreat ments and which does not similarly afiect the zinc sulfidparticles and permits the said zinc sulfid particles to floatsubstantially in the manner hereinbefore described.

2. A process for the preferential or selective separation of zincsulfids from lead sulfids in mixed sulfid concentrates obtained from anacid flotation separation which con- 7 sists in'submitting the saidconcentratesto agitation and aeration in a solution which does notchemically or otherwise permanently affect the lead sulfid particlesupon their surface but does by the action of the medium itself bring thesurface of the lead sulfid particles into direct contact with the saidmedium and wets the said leadsulfid particles whereby the said leadsulfid partiso i from an acid flotation separation which conagitationand aeration in a heated solution of common salt of such a strength asto preferentially wet said lead sulfids obtain-,

ing float concentrates relatively high in zinc on the one hand andresidues relatively high in lead on the other hand substantially in themanner hereinbefore described.

5. A process for the preferential or selective separation of zincsulfids from lead sulfids in mixed sulfid concentrates obtained by anymethod of concentration Which consists in submitting the saidconcentrates to agitation and aeration in a feebly acidulated solutionof common salt of such a strength as to preferentially Wet said leadsulfids obtaining floatconcentrates relatively high in zinc on the onehand and residues relatively high in lead on the other handsubstantially in the manner hereinbefore described.

6. A process for the preferential or seagitation and aeration in aheated and feebly I acidulated solution of common salt of such astrength as to preferentially wet said lead sulfids obtaining floatconcentrates relatively high in zinc on the one hand and residuesrelatively high in lead on the other hand substantially in the mannerhereinbefore described.

7. A process for the preferential or selective separation of zincsulfids from lead sulfids in mixed sulfids concentrates obtained by anymethod of concentration which consists in submitting the saidconcentrates to agitation and aeration in a feebly acidu'lated solutionof common salt of such a strength as to preferentially Wet said leadsulfids with the addition of an organic frothing agent -obtaining floatconcentrates relatively high in zinc on the one hand and residuesrelatively high in lead on the other hand substantially in the mannerhereinbefore described.

In testimony whereof I aflix my signature in presence of two witnesses.

LESLIE BRADFORD. Witnesses:

, CHARLES STANLEY BURGESS,

WINNIFRED WING.

